Authors
Vasyl Ustimenko
Faculty of Mathematics, Physics and Computer Science Maria Curie-Skłodowska University Plac Marii Curie-Skłodowskiej 1 PL-20-031,, Lublin, POLAND
© 2018 Vasyl Ustimenko, published by Slovak Academy of Sciences, Mathematical Institute
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.